This invention relates to buoyant, towed electrodes of the cable type such as are used for sweeping of magnetic influence mines and more particularly to improved constructions therefor.
U.S. Pat. No. 3,940,732, issued to J. A. Hudson and M. J. Yelverton and assigned to the assignee hereof, describes a buoyant electrode of a cable type that is towed along its axial length, by a helicopter for example, at substantial speeds through sea water. The electrode is energized to produce electrical currents in the sea water. Magnetic disturbances resulting from the electrical currents and the forward motion of the electrode are effective in sweeping magnetic influence mines. The electrode of that patent comprises a core of central strength member in the form of a synthetic filament rope, a cylindrical buoyant sleeve of a closed cell plastic foam material and an outer conductive layer formed of helically wound strands of alunimum wire. The aluminum wire strands are tightly bound with an aluminum wire serving in the forward portion of the electrode, and the forward end of the electrode is provided with a conductive metal lug or connector that is swaged or otherwise fixed to the strength member and provides for electrical connection to the serving and to the helical wires of the electrode. At the aft end of the electrode, the helical wires are bound to the buoyant sleeve by one of more metal bands, preferably of the screw tightened variety.
Variations from the electrode described in that patent are disclosed in U.S. Pat. Nos. 4,117,447 and 4,185,264, which variations are principally directed to structures for alleviating or reducing the phenomena referred to as "birdcaging" which is characterized by a ballooning of the helically wound layer of soft-drawn aluminum wires at the aft end of the electrode. The approach of U.S. Pat. No. 4,117,447 requires an axially keyed, sliding member, while that of U.S. Pat. No. 4,185,264 requires towing or "preconditioning" of the electrode. Elimination of both would, of course, be desirable.
In all of the foregoing electrode cables, there is provided a terminal lug which serves both as the leading tow point and also as the electrical connection to the towing cable through which the electrically energizing current is applied. That lug has typically comprised a tubular portion that is compressively swaged over a cable anchor of the type comprising a tapered bore in which the strands of the strength member of the cable are splayed and potted and in part over a wire serving that binds the forward ends of the layer of aluminum electrode wires. Thus, the lug makes both mechanical and electrical connections. It has been found in practice that, it becomes necessary from time to time to replace the lug because of damage by electrolysis, mechanical fatigue, and the like. This replacement requires cutting the old lug and anchor off, trimming the electrode cable back, and applying a new anchor, serving, swaged lug, and rubber collar.
In one configuration of use for minesweeping purposes electrodes cables, which are made up in standard lengths of say 175 feet and diameters on the order of 5 inches, are streamed from a towing vehicle carrying D.C. generating means and various electronic instrumentation. One electrode serves as a cathode and is connected in a close-coupled manner relative to the vehicle by a short pigtail cable while a second electrode serves as an anode and is connected to the aft end of a long, insulated supply cable. In this configuration it has been found that the electromagnetic field generated by the forward end of the close-coupled cathode interferes with operation of the mentioned instrumentation. While increasing the length of or adding to the short pigtail cable to move the cathode rearwardly eliminates the interference problem, there are introduced considerable added logistics problems of handling, storage, and deployment due to the extra pigtail cable.